On account of increased performance requirements, modern cast pistons, in particular light-alloy pistons, often have a cooling duct, which is produced during the casting by a core, in particular a sand or salt core. After the molten material has solidified, the core is washed out again and thus leaves behind the desired cooling duct. In order also to be able in addition to absorb better the high loads occurring on piston rings, the aforementioned light-alloy pistons often have cast-in ring carriers, in particular of cast iron, in which the later piston ring can be arranged. When fitting such a ring carrier or a salt or sand core in casting moulds for light-alloy pistons, the problem often arises that the ring carrier is the temperature-critical component. There is the risk of internal thermal stresses occurring in the later piston at the interface with the ring carrier. The sand or salt core, on the other hand, is fragile and must be mechanically handled with extreme care. For this reason, previously the core was inserted into the casting mould first and the ring carrier last, before the molten material was introduced. This makes the cooling time for the ring carrier shorter.
The core was often grasped from outside with gripping tongs, the sequence causing a geometrical restriction in that the core inserted first must not protrude into the later path of insertion of the ring carrier. Therefore, above the ring carrier, the core must not under any circumstances reach the inner radius thereof, while at the same height a certain distance must remain as the wall thickness. Only below the ring carrier would there be no constraints. However, there is also increasingly a desire for high-level cooling ducts, for which the salt core overlaps the ring carrier. This makes the placing process of the core and the ring carrier even more complex.
DE 10 2013 206 708 A1 discloses an apparatus of the generic type for producing a piston for an internal combustion engine by casting, the piston containing a cooling duct and the apparatus comprising the following components: a fixed mould with an upwardly open cavity, in which a core serving for forming the cooling duct can be arranged, a movable mould, which is arranged in a vertical direction in relation to the fixed mould and comprises a predetermined engaging part, a guiding mould including an engaging part, which can engage in the fixed mould and has the same form as the engaging part of the movable mould, and also a core holding mechanism, which is arranged in the guiding mould, in order to hold the core, for example a salt or sand core, at a predetermined position. However, a disadvantage of this apparatus is that the mechanically extremely sensitive core is gripped by prestressing from the inside, whereby in particular C-shaped cores, that is to say cores that do not form a closed ring, can break particularly easily.